Find local political/nonprofit groups and ask them what you can do to help. They will probably have a tonne of ideas with no idea how to implement them. Their ideas may not all be good, but as long as you've reached out to groups who have a track record of being effective, they're probably better than yours/mine. If you want to dig even deeper, try and really understand what they're doing and use your knowledge of what is possible to find opportunities they didn't know existed.
I spent this afternoon readings about housing policy and one of the nonprofits literally said on their website that they were seeking funding to do web development for an interactive visualisation. Is this the most effective way of using dev resources? No idea; maybe these visualisations help them influence decision makers in this area, but it's a start if you're really keen.